class Solution {
public:
    int tribonacci(int n) {
            if(n <= 1) // 处理边界
                return n;
 
            vector<int> dp(n+1, 0);
            dp[1] = dp[2] = 1;
            for(int i = 3; i <= n; ++i)
            {
                dp[i] = dp[i-1] + dp[i-2] + dp[i-3];
            }
            return dp[n];
    }
};